The present invention relates to inorganic matrix compositions, which incorporate a silicate network and which can be processed at conditions comparable to those used for typical high-performance organic polymer processing, i.e., temperatures of about 15° C. to about 200° C. and pressures of less than about 200 psi, although a wide range of temperatures and pressures can be employed. The physical and thermal properties of the inorganic matrix binder, as well as composites, may be enhanced by elevated processing temperatures (up to 400° C. and greater) and pressures (up to 20,000 psi and greater) to produce exceptional composites and neat resin components. The composite materials formed at the lower processing conditions exhibit excellent thermal, dimensional, physical and flameproof properties.
Inorganic matrices are useful as flame retardant binders, bulk materials, adhesives, cellular materials, such as foamed materials, or composite materials. As bulk materials, they are used to form shaped objects which when cured provide a structural material. As a composite material, the matrix composition is used to impregnate a fabric, which may be combined with other similarly impregnated fabrics, to form the composite lay-up, which is then shaped and cured to form a shaped object, similar to a bulk material, but with the benefit of the reinforcement provided by the fabric.
The basic concept of composite materials has been known for centuries. Composite materials offer a unique blend of value added features, such as weight savings, electrical insulation, thermal insulation, corrosion resistance, and manufacturing cost savings. These features in some instances can overshadow the material cost in specialized applications ranging, for example, from sporting equipment to the F-22 aircraft fuselage. However, current state-of-the-art composite materials can also exhibit properties that present serious barriers to entry in some high-performance markets. These include poor flame, smoke and toxicity (FST) performance, physical degradation at high temperatures as well as higher material and processing costs. When exposed to fire or temperatures greater than about 500° C., conventional composite materials can combust and generate toxic smoke and/or gases. The exceptions, such as ceramic matrix composites and metal matrix composites, are too expensive (often more than $500/lb) to gain a significant market presence. Clearly, a market need exists for affordable high temperature-resistant, composite insulating structures.
The most familiar composite systems today are based on organic polymer matrices such as epoxy/glass fiber, epoxy/carbon fiber, polyurethane/glass fiber, PVC/glass fiber, polyimide/quartz fiber, polyester/glass fiber and nylon/glass fiber. Although organic polymer composites exhibit excellent physical and mechanical properties, they are limited with regard to flammability, smoke and gas generation and elevated service temperatures. The flammability of organic polymer-based composites can be reduced by the addition of inorganic components and/or additives. The substitution of hydrogen atoms with halogen atoms (such as for example, chlorine) in hydrocarbons and hydrocarbon polymers can significantly reduce flammability and smoke/gas generation but will degrade at temperatures greater than 250° C. and eventually incinerate at temperatures greater than 450° C. Organic thermoplastic polymers also deform at relatively low temperatures (about 100° C.–300° C.) and organic polymers designed for higher service temperatures are generally prohibitive in material and processing costs.
Other composite materials include metal matrix composites (MMC), ceramic matrix composites (CMC), carbon-carbon composites as well as other inorganic matrix composites. A composite matrix may be 100% inorganic, or it may contain some organic content. Inorganic matrix networks include ceramics, silicates, glasses, aluminum silicates, alkali aluminum silicates, potassium silicates, sodium silicates, silicon carbides, silicon nitrides, boron nitrides, alumina, cementitious materials, metals, metal alloys or other matrix materials known to those knowledgeable in the arts. Other materials can be considered include inorganic particles encapsulated with inorganic binders, organic resins filled with inorganic fillers, inorganic-organic hybrids such as silicone, and other inorganic matrix materials known to those knowledgeable in the arts.
A disadvantage of organic polymers is their deficiencies at high temperatures. The use of metals and ceramics raises additional questions with regard to thermal and electrical conductivity, weight limitations, toughness, dielectric properties, ductility, and processing options. Further, ceramics do not lend themselves to the low temperature processing procedures as contrasted with organic polymer processing.
Alkali silicates are employed as affordable inorganic matrix binder materials. See for example, U.S. Pat. Nos. 4,472,199; 4,509,985; 4,888,311; 5,288,321; 5,352,427; 5,539,140; or 5,798,307 to Davidovits; U.S. Pat. No. 4,936,939 to Woolum; or U.S. Pat. No. 4,284,664 to Rauch. However, alkali silicates typically possess a very high pH. Thus these alkali solutions are so caustic that they frequently damage glass fibers, severely degrading its strength. Furthermore, the cured composites prepared in accordance with these patents still exhibit a high pH in a solid form.
A need exists for noncombustible, temperature-resistant inorganic polymer compounds which process at temperatures and pressures typical for organics (<200° C. and <200 psi) that combines the desirable features of ceramics (non-flammability, resistance to temperatures >450° C.) and organic polymers (low-temperature processing, complex shapes).